Declining reproductive output in capercaillie and black grouse – 16 countries and 80 years

Abstract

Declines in populations of capercaillie (Tetrao urogallus) and black grouse (Lyrurus tetrix) have been reported from both Central Europe and the continuous boreal forests of Fennoscandia. While intensified land-use is assumed to be the underlying cause of these declines, the mechanisms are not yet understood. Predation is the proximate cause of mortality of eggs, chicks and adults throughout capercaillie and black grouse ranges, but the link between predation and habitat and/or climate change remains unclear. To investigate temporal trends in reproductive output of woodland grouse, we collated previously published and unpublished data of reproduction in capercaillie and black grouse throughout their ranges from 1930 to 2012. We show that, overall, reproductive success has decreased and stabilized at low levels in most regions whilst capercaillie reproductive output in Scotland is still declining. With today's net reproduction, capercaillie and black grouse adult survival is too low to compensate for reproduction declines. Consequently, populations are expected to further decline unless reproductive performances improve. We put our findings in the context of changes in land use, climate and generalist predator numbers. By critically reviewing how these factors limit reproductive success in capercaillie and black grouse, we hope to shed light on the underlying mechanisms causing the decline. Our results imply that measures should be undertaken to reduce mortality of capercaillie and black grouse chicks and eggs. We suggest that future studies should aim to better understand which predators limit capercaillie and black grouse populations and how predation rates are mediated by continuously changing habitat and climate.

Phenology largely explains taller grass at successful nests in greater sage‐grouse

“…For example, increased vegetation height and/or greater insect abundance resulting from reduced grazing intensity positively affected production in black grouse ( Tetrao tetrix ) in Britain (Baines, ; Calladine, Baines, & Warren, ). The positive effect on production was, however, diminished or even reversed when grazing reduction treatments covered larger areas (Calladine et al., ), suggesting mosaics of vegetation height may confer greater benefits than uniformly tall vegetation (also see Baines, Richardson, & Warren, ; Jahren, Storaas, Willebrand, Moa, & Hagen, ). Taller vegetation may also moderate thermal extremes experienced by grouse, a function which may take on increased importance under climate change (Hovick, Elmore, Allred, Fuhlendorf, & Dahlgren, ).…”

Range loss of a threatened grouse species is related to the relative abundance of a mesopredator

“…Predation can be an important cause of chick mortality in capercaillie, but especially if suboptimal conditions predispose chicks to predation (Wegge and Kastdalen , Jahren et al. ), representing a potential threat for grouse population development in a changing climate (Jahren et al. ).…”

“…), representing a potential threat for grouse population development in a changing climate (Jahren et al. ). By contrast, the negative effect of fox abundance in our models was mitigated by otherwise optimal conditions resulting in high persistence probabilities regardless of fox abundance (Fig.…”

“…Grouse, in particular black grouse ( Lyrurus tetrix ) and capercaillie ( Tetrao urogallus ), are species of major conservation concern in Europe (Storch , Jahren et al. , and references therein). Populations are currently characterized by low reproductive success (Jahren et al.…”

“…Populations are currently characterized by low reproductive success (Jahren et al. ) and range contractions (Storch ). It is well known that reproductive success in grouse is reduced at high predator abundance (Marcström et al.…”